1. Field of the Invention
This invention relates to novel KA-6643-series antibiotics and salts and esters thereof, their preparation, medical compositions comprising same, and a microorganism capable of producing same.
2. Prior Art
The present inventors have already found a process in which a strain referred to as Streptomyces sp. KC-6643 that has been isolated from soil is cultured, from which there are isolated and collected antibiotics KA-6643-A and KA-6643-B each showing an excellent antibacterial activity against both gram-positive and gram-negative bacteria and a .beta.-lactamase inhibiting activity. These substances as well as the process are disclosed in Japanese Laid-open Patent Application Nos. 55-139380 and No. 56-43284.
The present inventors have conducted a further investigation on culture broths of a strain of Streptomyces sp. KC-6643 and its mutants. They have found that novel antibiotics other than the substances KA-6643-A and KA-6643-B are produced in the culture broths and have succeeded in isolating such antibiotics from the culture broths.